Keywords

1 Introduction

The ship lifts play an important role in river channelization and communication of different water systems in inland water transportation. Compared with ship locks, ship lifts have obvious advantages, especially suitable for high dam navigation, canal navigation between different water systems. The process of ship entering and exiting the ship lift chamber is one of the core links of the whole process of the ship lift operation. Due to the high blockage ratios of the ship lift chamber, the hydraulics problem becomes a complex three-dimensional water flow problem coupling with ship operation. To prevent the ship from touching bottom it is necessary to formulate reasonable ship draught control standards and ship navigation methods based on the ship squat and the water fluctuation of the ship lift chamber, so as to ensure the safety of ship navigation and ship lift docking.

Some scholars proposed the practical methods for calculating the squat with the general ship characteristics (Tuck 1973; Husska 1976; Eryzulu 1978; Icorels 1980; Barrass 1981; Norrbin 1985; Millward 1990; Millward 1992; Eryzulu, 1994; Gourlay 2008;). Bao (Bao 1991) presented the formula of maximum squat in ship exiting the chamber according to the previous studies in China. The German Federal Waterway Design and Research Institute carried out the field investigations and the numerical calculation on the extra-large ships entering and exiting the Lüneburg ship lift. NHRI (Hu et al. 2011) advanced the formula of Bao based on the experiments of the Three Gorges ship lift.

The current studies at home and abroad mainly combine with the concrete engineering lack of the universality. In addition, most of them uses the formulas of ordinary restricted channels to make calculations, without considering the plane dimension influence of narrow navigation, enclosure and so forth.

In conclusion, this paper introduces the docking process of different types of ship lift, and systematically summarizes the scientific problems involved in the docking process when the ship enters and leaves the tank. Explain in detail the variation law of the ship’s sailing resistance characteristics during the process of entering and leaving the tank. Describe the variation law of water surface fluctuation in the tank during the process of ships entering and leaving, analyze the relationship between the fluctuation characteristics and the ship speed, cross-section coefficient, entering or leaving, the water level in up-and downstream docking process. Summarizes the variation characteristics of water surface in the tank. Introduce the main influencing factors of ship squat, including ship size, ship draught, ship speed, tank size, tank water depth, etc. Research results and the relevant empirical formulas are summarized in chronological order according to different research methods. Outline the impact of the ship’s entering and leaving of the tank on the characteristics of tank’s load change and the force characteristics of the ship lock mechanism.

2 The Docking Process of Ship Lifts

Ship lifts come in a variety of classifications. According to whether the ship tank going into the navigation pool or not, it can be divided into two types: tank-launching ship lift and non-tank-launching ship lift. For the non-tank-launching ship lift, the upstream and downstream docking processes are consistent. For the tank-launching ship lift, the upstream docking process is the same as that of the non-tank-launching ship lift, but the downstream docking process is special.

The tank of the tank-launching ship lift enters the downstream approach channel directly, eliminating the need of the lower lock heads and its corresponding equipment, which not only saves the quantity of work, but also eliminates some auxiliary equipment such as retaining and sealing mechanism; meanwhile, the procedure of the process is greatly reduced, the time ships take to pass the dam is shortened, the operational reliability, passing capacity and operational efficiency are all increased a lot, compare to the non-tank-launching ship lift. The main factors affecting the hydrodynamic characteristics of tank-launching ship lift’s process which tank going in and out the navigation pool is: the shape of the ship lift’s tank, the size of the navigation pool, the speed of the tank going in and out, and the size of the approach channel.

The docking process between the ship and the upstream and downstream is an important part of the whole process of the ship lift operation. It involves problems like the hydrodynamic characteristics of the ship lift’s tank when the tank’s door is opened and closed; the ship navigation conditions and hydrodynamic characteristics in the tank during the process of ships entering and leaving; the change affections of downstream unsteady flow on the operation of the ship lift and other related hydrodynamic problems.

3 The Process of Ships Entering Leaving the Tank of a Ship Lift and its Hydraulic Problems

During the ship entering the tank, the bow kept pushing the water flow into the tank, which leads to the water level of tank gradually rises, and the water level of the stern lowers, forming a fore and aft water level difference, causing reverse flow of water on the ship’s side and the bottom of the ship. The ship trim and sink then appears. When the ship completes the entrance and parks in the tank, the water surface decreases due to the inertia of the flow in the tank, yet the stern water is connected to the channel, with the supplement by the channel water, the water level drops less, and the stern sinks. During the ship leaving the tank, the bow water is connected to the channel, the bow kept pushing the water flow into the channel and the water level in the tank gradually decreases. Although the approach channel replenishes the water in the tank, but because of the ships blocking while the water in the stern is small, water supply insufficient, the water level drops more obviously, and the stern sinks is also larger.

The safety of the ship in the tank is one of the most concerned issues in the design and research of the ship lift as the cross-section coefficient of the tank is small. It is necessary to determine the reasonable water depth of the tank and the way of ships’ navigation to prevent the bottoming and the drastically changing of the tank’ load when the ships entering and leaving the tank, and to ensure the safety of the ship and the tank. Using the combination method of mathematical model and physical model and real ship test, the hydrodynamic characteristics of the ship entering and leaving the ship lift at different speeds are studied to determine the reasonable water depth of the tank and provide a basis for reasonable navigation.

Using the combination method of mathematical model and physical model and real ship test, the hydrodynamic characteristics of the ship entering and leaving the ship lift at different speeds are studied to determine the reasonable water depth of the tank and provide a basis for reasonable navigation (Figs. 1 and 2).

Fig. 1.
figure 1

Schematic diagram of three typical moments of ship entering the tank

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Fig. 2.
figure 2

Schematic diagram of three typical moments of ship leaving the tank

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4 Hydrodynamics Study of Ships Entering and Leaving the Tank

4.1 Characteristics of Ship’s Sailing Resistance

During the process of ship entering and leaving the tank, the ship’s navigation environment is narrow and shallow, which lead to the flow field around the hull presents obvious bank effect and shallow water effect. The total resistance, lateral force, pitching moment and turning moment of the ship increase as the speed of the ship increases, and the speed of the ship has a significant impact on the force of the ship. Therefore, from a safety perspective, it is recommended that the ships enter and leave the tank at a lower speed. Meanwhile, when the ship enters the approach channel from the open water, the asymmetry of the flow field on both sides of the ship increases due to the narrowing of the water on both sides of the ship, which result in the rapid increase of lateral force and the turning moment. Therefore, it is more likely hit the wall or turn when ship sailing at this moment. Anti-collision measures can be considered in practical work.

4.2 Characteristics of Water Surface Fluctuation in the Tank During the Process of Ships Entering and Leaving

When the ship leaves the tank, the water pushed out by the ship in the rear of the stern can only be replenished by the narrow space around the ship and the tank, resulting in a drop in the depth of the tank and the channel behind the ship. Obviously, the closer to the approach channel, the greater the maximum drop in the water surface, and the maximum drop in the water surface in the tank basically occurs before the bow completely leaves the tank. When the ship enters the tank, the distribution of the fluctuation of the water surface in the tank is opposite to that of the ship’s leaving. The closer to the closed end of the tank, the greater the fluctuation of the water level, and the maximum drop in the water surface of the tank appears after the ship enters the tank. The ship speed in and out of the tank has a greater impact on the maximum reduction of the tank’s water surface. The maximum decrease in the water surface increases as the speed of ship increases.

4.3 Characteristics of Ship Squat During the Process of Ships Entering and Leaving

The ship’s speed has a significant impact on the ship squat. At the same speed, the squat of the ship when leaving the tank is larger than that when entering the tank. Therefore, the ship squat when sailing out of the tank is the safe control condition for the ship to enter and leave the tank without the bottoming. As the tank’s water depth decreases, the ship squat also decreases, the influence of the tank’s water depth is less than the impact of the ship’s speed on the squat. Under the same depth of the tank and the speed of the ship in and out, the larger the ship’s tonnage, the smaller the section coefficient of the tank, and the greater the squat of the ship (Fig. 3).

Fig. 3.
figure 3

Schematic diagram of ships leaving chamber

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The relationship between the maximum squat of the ship (\(\delta\)), entering and leaving the tank, and the water depth (H), section coefficient (n), and speed of the ship (V) can be expressed by two dimensionless quantities:

$$P = \frac{\delta }{H},\,K = \frac{{V^{2} }}{2gH} \times \left[ {\left( {\frac{n}{n - 1}} \right)^{2} - 1} \right]$$
(1)

in the range of 0.3–1.0 m/s, the maximum squat of the ship is basically linear with the square of the ship speed out of the tank (Fig. 4).

Fig. 4.
figure 4

Relationship of ship squat of different ship lifts

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4.4 Force Characteristics of the Ship Lock Mechanism

During the process of upstream and downstream docking, ship’s entering and leaving the tank, the two groups of locks at the same end of the tank are subject to fluctuations in force and amplitude, and the amplitudes of the lock mechanisms at the upper and lower ends are greatly different, the fluctuation near the closed end of the tank is large, and on the other end is small. It is necessary to pay attention to the impact of downstream water level fluctuation on the load of the ship. Because the downstream water level changes too fast, when the ship is docked with the downstream, the water level between the tank and the downstream waterway may form a difference, resulting in the water loss or full water of the tank. At this time, the four locking mechanisms are significantly more stressed than the docking state of the upstream side, and may even exceed its acceptable range. Therefore, before opening the door of tank, it is necessary to confirm whether there is a water level difference between the downstream and the tank.

4.5 The Design Criteria for the Water Depth of the Ship Lift’s Tank

China’s “Inland Navigation Standards” (GB50139-2004) stipulates the standard water depth (H) of the tank as calculated by the following formula:

$$H = T + \Delta H$$
(2)

In the formula: T- the standard draught of the ship; ΔH- the additional depth, which is the sum of the ship squat and safety margin without bottoming.

In the “Inland Navigation Standards”, the value of the safety margin without bottoming is not clearly stated. Factors that should be considered for the additional depth of the ship: the ship will increase the draught when sailing in shallow water; the unevenness of the tank bottom; the sinking of the stern when the ship leaves the tank. Therefore, the safety margin of the tank should generally be not less than 0.5–0.6 m.

For the 500t class ship lift (designed ship draught 1.6 m) and the 1000 t class ship lift (designed ship draught 2.0 m) to ensure that the minimum normal design water depth of the corresponding tank is 2.5 m or 3.0 m, the safety margin of the tank is 0.5–0.6 m, the design speed of the ship out of the tank should be less than 0.6–0.8 m/s. Considering the misloaded water depth of the tank, which the limit should not exceed −0.2 m, the speed of the ship out of the tank should be controlled at 0.6–0.7 m/s.

After the ship’s speed exceeds 0.7 m/s, the ship’s tilting moment caused by the fluctuation of the water surface in the tank increases rapidly. When the ship’s entering speed is around 0.8–0.9 m/s, the ship’s tilting moment peaks. Therefore, considering the safety margin, the longitudinal tilting moment of the tank, the maximum speed of the ship entering the tank should not exceed 0.7 m/s.

5 Conclusion

After years of research, the general formula of calculating the maximum ship squat when ships entering and leaving the tank is established by NHRI. Meanwhile, the mooring force in ship lift tank when the reclining door is opened and closed is established which reveals the unsteady flow influence on safe operation of ship lift mechanism. Putting forward ship lift docking control method to assure the safety of ships and the ship lift which include the reclining door opening and closing speed and water depth control standards, solved the hydrodynamic safety issues when ship entering and leaving the tank of a ship lift.